EP0620499B1 - Photopolymerisable material and process for making colour image - Google Patents

Description

The invention relates to a photopolymerizable material which is suitable for producing colored images, in particular for color testing for multi-color printing. It also relates to a method for producing a colored image, in particular a color test method, in which a photopolymerizable material composed of a transparent carrier film, a colored polymerizable layer and a thermoplastic adhesive layer is laminated to an image-receiving sheet, exposed imagewise through the carrier film and pulled together by peeling off the carrier film is developed with the exposed areas of the colored polymerizable layer to form an image.

Such materials and processes are known and are described, for example, in US Pat. Nos. 4,895,787 and 5,049,476. The process has the great advantage that no alkaline or acidic solutions and no organic solvents are required to develop the image. These materials consist of a transparent carrier film, a colored photopolymerizable layer and a heat-activated adhesive layer. A disadvantage of these materials is that they provide images whose background areas are yellow. As was found, this discoloration is mainly due to the photoinitiator contained in the photopolymerizable layer, which can diffuse into the adhesive layer during storage. Since this is also contained in the image areas of the photopolymerizable layer, the color of each individual color image is falsified by its presence. Attempts have been made to use photoinitiators whose absorption lies exclusively in the ultraviolet and which therefore appear colorless in the visible range. However, these photon initiators are much less effective in the light of conventional copying lamps and require very long exposure times. It was also found that itself a color shift can occur with visually colorless photoinitiators, since these compounds often provide colored light decomposition products.

US Pat. No. 3,615,435 describes a process for producing colored images in which a light-sensitive material comprising a layer support, an undyed photopolymerizable layer, a colored photopolymerizable layer and an image-receiving sheet is exposed imagewise and developed by pulling it apart to form the image. The unexposed areas of the colored photopolymerizable layer remain on the image-receiving sheet, while the exposed areas remain on the support. In this way, monochrome images are obtained. The production of multicolor images from superimposed partial color images is also described. Here, however, the development is always carried out by washing out. This material also undergoes a color shift in that the colored photopolymerizable layer contains a photoinitiator.

A similar photosensitive material is described in US Pat. No. 4,288,525, which has an undyed photopolymerizable layer and a colored, non-photosensitive layer. The material is exposed and developed by pulling it apart. The photopolymerizable layer and at least part of the colored layer remain on the support at the exposed areas, while both layers remain on the image-receiving material at the unexposed areas. Here too, the color is falsified by the photoinitiator of the photopolymerizable layer in the colored positive image. A similar material and process is described in US-A 4,692,395.

The object of the invention was to propose a photopolymerizable material and a method for producing colored images, in particular multicolored images, which allows color-pure images to be produced which are not by photoinitiator residues, which absorb in the visible spectral range, are falsified, but which nevertheless allows the use of highly light-sensitive photopolymerizable mixtures.

• (A) einer flexiblen, transparenten Trägerfolie,
• (B) einer farbigen, polymerisierbaren Schicht, die ein polymeres organisches Bindemittel, eine radikalisch polymerisierbare Verbindung mit mindestens einer endständigen ethylenisch ungesättigten Gruppe und einen Farbstoff oder ein Farbpigment enthält, und
• (C) einer Haftschicht, die ein thermoplastisches Polymeres enthält und ein Tg von 25 bis 100 °C aufweist.

The invention is based on a photopolymerizable material

• (A) a flexible, transparent carrier film,
• (B) a colored, polymerizable layer which contains a polymeric organic binder, a free-radically polymerizable compound having at least one terminal ethylenically unsaturated group and a dye or a color pigment, and
• (C) an adhesive layer containing a thermoplastic polymer and having a Tg of 25 to 100 ° C.

The material according to the invention is characterized in that the layer (B) contains no photoinitiator, that between the carrier film (A) and the colored polymerizable layer (B) there is an uncolored photopolymerizable layer (D) which is a polymeric organic binder, a radical one contains polymerizable compound having at least one terminal ethylenically unsaturated group and a photopolymerization initiator, and that the cohesion of layers (B), (C) and (D) and the adhesion of these layers to one another and to the carrier film (A) are adjusted so that the Adhesion (a ₂ ) of the photopolymerizable layer (D) to the colored polymerizable layer (B) in the unexposed state is smaller than the adhesion (a ₃ ) of the colored layer (B) to the adhesive layer (C) and the adhesion (a ₁ ) the photopolymerizable layer (D) on the carrier film (A) and as the cohesions (c ₁ ), (c ₂ ) and (c ₃ ) of the layers (D), (B) and ( C) and that the adhesion (a ₃ ') of the colored layer (B) to the adhesive layer (C) in the exposed state is smaller than the adhesion (a ₁ ') of the photopolymerized layer (D) to the carrier film (A) and Adhesion (a ₂ ') of the photopolymerized layer (D) to the colored layer (B) and as the cohesions (c ₁ '), (c ₂ ') and (c ₃ ') of the layers (D), (B) and (C).

According to the invention, a process for producing a colored image is further proposed, which is characterized in that a photopolymerizable material of the above-mentioned nature is laminated with its adhesive layer (C) under pressure and at elevated temperature on an image-receiving sheet (E), the laminate obtained by exposing the carrier film (A) imagewise and peeling the carrier film together with the photopolymerizable layer (D) and the exposed areas of the colored polymerizable layer (B) from the image-receiving sheet, the adhesion of the adhesive layer (C) to the image-receiving sheet (E) in unexposed state (a ₄ ) is greater than the adhesion (a ₂ ) of the photopolymerizable layer (D) to the colored layer (B) and in the exposed state (a ₄ ') is greater than the adhesion (a ₃ ') of the colored polymerizable layer Layer (B) on the adhesive layer (C).

The method according to the invention is preferably carried out to produce a partial color image with a material which contains a colored polymerizable layer (B) in a basic color of multicolor printing and is exposed under a color separation which corresponds to the same basic color. In particular, the described method steps can be repeated on the same image receiving sheet with materials in the other primary colors, the exposure taking place in each case in the register with the first partial color image present on the receiving sheet.

It is an essential feature of the material according to the invention that the colored layer (B) contains a polymerizable compound but no photoinitiator. This ensures that no photoinitiator can diffuse from this layer into the immediately adjacent adhesive layer. The colored picture elements transferred to the image receiving sheet also contain practically no portions of photoinitiator which could distort their color impression. It is also essential that the layer (B) contains a polymerizable compound which is at least in the border area to the photopolymerizable Layer (D) upon exposure to contact with the polymerizing compound in this layer is also stimulated to polymerize and thereby increases the adhesion between the two layers. It is not known exactly how far the polymerization continues into the colored layer; in any case, it results in a substantial increase in the adhesion between layers (B) and (D).

In the accompanying drawing, a photopolymerizable material according to the invention is shown in cross section after lamination to an image receiving material (E). In the right part of the figure, the material is shown after exposure, indicated by arrows, in the left part an unexposed area. A and E denote the carrier film and the receiving material. The undyed photopolymerizable layer (D), the colored polymerizable layer (B) and the adhesive layer (C) are arranged between them. C ₁ denotes the cohesion of the photopolymerizable layer, c ₂ that of the colored polymerizable layer and c ₃ that of the adhesive layer. Adhesion to the various interfaces before exposure is indicated by a ₁ , a ₂ , a ₃ and a ₄ , adhesion after exposure by a ₁ ', a ₂ ', a ₃ 'and a ₄ ' in the sense of the above explanations . The hatching of the layer (D) and the boundary zone within the layer (B) in the exposed part indicates the effect of the polymerization.

Before exposure, the lowest adhesion (a ₂ ) is between layers (D) and (B). All other guarantees, like all cohesions, are stronger than (a ₂ ). The position of the slightest adhesion is shifted by the exposure since, as described above, the layers (D) and (B) are anchored more firmly to one another by the polymerization. Now there is the lowest adhesion (a ₃ ') between layers (B) and (C), which is again lower than each of the cohesions c ₁ ', c ₂ 'and c ₃ '. The dashed lines each show the boundary line of least liability, ie the predetermined breaking point when pulling apart (A) and (E). Although the cohesion of the layer (D) and partly of the Layer (B) changed during exposure, this change has no influence on the position of the predetermined breaking point.

In the context of this invention, an uncolored photopolymerizable layer is a layer which is not colored by the addition of dyes or color pigments which absorb in the visible spectral range. As already stated, the colored polymerizable layer (B) itself is not photosensitive; however, when the neighboring photopolymerizable layer is exposed, it can be stimulated to polymerize at least in the contact area with it. After the transfer of the image areas to the receiving sheet, the layer can also be post-cured by intensive exposure without an original, possibly with heating.

Suitable flexible transparent carrier films (A) for the material according to the invention are, in particular, those plastic films which are dimensionally stable when heated to about 60 to 130 ° C. Films made of polyesters, polycarbonates, polyimides and similar polymers are preferably used for this purpose; Polyester films are generally preferred. The carrier film can have a thickness in the range from approximately 10 to 120, preferably from 20 to 80 μm. To improve dimensional stability, the films are generally stretched biaxially and, if necessary, heat-set. The surface of the film can be smooth or matt, smooth films are mostly preferred. To improve the adhesion of the photopolymerizable layer (D), the surface can be subjected to a treatment which increases the adhesion, for example by corona discharge, by etching with chemicals, for example trichloroacetic acid, and by coating with an adhesion-promoting underlayer. Such coatings are generally 0.001 to 0.1 microns thick. They can consist of copolymers of (meth) acrylic acid esters, such as are described, for example, in US Pat. No. 4,098,952, and are preferably crosslinked. Suitable films are described in US-A 5,049,476.

The essential constituents of the photopolymerizable layer (D) comprise a polymeric binder, a polymerizable compound, a photoinitiator and, if appropriate, other customary additives. The binders include Homo- and copolymers of (meth) acrylic acid esters and especially polyvinyl acetals, e.g. Suitable for polyvinyl butyral, regional or formal. The proportion of the binder is generally 10 to 75, preferably 30 to 70,% by weight, based on the nonvolatile constituents of the layer.

The polymerizable compound contains at least one, preferably at least two terminal ethylenically unsaturated groups. (Meth) acrylic esters of polyhydric, in particular primary aliphatic or cycloaliphatic alcohols are particularly preferred. The compound should have a boiling point of at least 100 ° C at normal pressure. Examples of suitable compounds are acrylates and methacrylates of triethylene glycol, tripropylene glycol, tetraethylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaervthritol and of bisphenol A or trimethylolpropane reacted with ethylene oxide or propylene oxide. The polymerizable compound is generally present in the layer in a proportion of 10 to 60, preferably 15 to 40,% by weight, based on the non-volatile constituents.
The photoinitiator is a compound that can be excited to form free radicals by irradiation with actinic light. Examples are multinuclear quinones, acyloins, in particular benzoins, for example benzoin alkyl ethers, α-alkyl-benzoins, triarylimidazolyl dimers, quinoxaline compounds and especially trihalomethyl compounds, especially trihalomethyl-s-triazines. The photoinitiator is generally present in the photopolymerizable layer in an amount of 2 to 30, preferably 5 to 20% by weight.

The layer can also contain inhibitors for thermal polymerization, spectral sensitizers, plasticizers, oligomers, and surface-active agents Contain compounds, inert fillers, optical brighteners, antihalation agents, photoactivators, hydrogen donors and residual solvents.

The photopolymerizable layer generally has a layer weight of 0.05 to 3, preferably 0.2 to 0.5 g / m ² .

The colored polymerizable layer (B) contains a polymeric binder, a polymerizable compound, a dye or a color pigment and, if appropriate, other conventional additives. The polymerizable compound may be the same as that contained in the photopolymerizable layer. It can also be another compound selected from the same general group and can be present in equal proportions. The other additives can also be the same as in the photopolymerizable layer.

Suitable polymeric binders are the same as in the photopolymerizable layer and additionally styrene / maleic anhydride, styrene / maleic acid semiester copolymers, polyamides, polyvinylpyrrolidones, cellulose derivatives such as cellulose esters and ethers, phenolic resins and polyvinyl esters. Polyvinyl acetals are also preferred here. The binder is generally present in an amount of 10 to 75, preferably 20 to 50% by weight, based on the nonvolatile fractions of the layer.

The dye or the pigment can, for example, permanent yellow G (CI 21 095), permanent yellow GR (CI 21 100), permanent yellow DHG (CI 21 090), permanent ruby L6B (CI 15 850: 1), permanent pink F3B (CI 12 433), Hostaperm Pink E (CI 73 915), Hostaperm Red Violet ER (CI 46 500), Permanent Carmine FBB (CI 12 485), Hostaperm Blue B2G (CI 74 160), Hostaperm Blue A2R (CI 74 160) and Printex 25 (carbon black). The pigments and dyes can be mixed if necessary to achieve the desired color. The pigments are generally mixed with a portion of the binder in a suitable manner Dispersed and pasted solvents. The average particle size is generally below 1 μm, preferably below 0.2 μm. Pigments are generally preferred over dyes. The dye or the pigment is usually contained in the layer in an amount of 10 to 50, preferably 15 to 35 wt .-%, based on the non-volatile constituents.

The colored polymerizable layer (B) generally has a layer weight of 0.1 to 5, preferably 0.3 to 1 g / m ² . It is generally made by coating and drying using solvents. If the solvents have little or no dissolving effect on the constituents of the photopolymerizable layer (D), the coating can be applied directly to this layer. Otherwise, the colored polymerizable layer can be applied from a solution to a temporary layer support, dried and transferred to the photopolymerizable layer by lamination.

The adhesive layer (C) contains a thermoplastic polymer and possibly other components. It has the property of becoming sticky when heated to a temperature in the range of 60 to 130 ° C. It is applied from solution or dispersion or by lamination to the colored polymerizable layer (B). Suitable solvents which do not dissolve layer (B) are saturated hydrocarbons, for example cyclohexane, n-hexane and n-heptane; Water or mixtures of water with miscible organic solvents. (Meth) acrylic acid copolymers with a high acid number or vinyl acetate / crotonic acid copolymers can be applied from aqueous, for example aqueous-ammoniacal solutions. Other polymers can be applied from aqueous dispersions, for example vinyl acetate polymers. Still other polymers can be applied from the melt, for example ethylene / vinyl acetate copolymers. The adhesive layer can also be applied to the colored polymerizable layer (B) in such a way that it is produced on a temporary support and from there through Laminating and peeling off the temporary support is transferred to the colored polymerizable layer.

The adhesive layer can also be transferred from the temporary support to the image-receiving sheet (E) by lamination and peeling. The photopolymerizable material comprising the carrier film (A), the undyed photopolymerizable layer (D) and the colored polymerizable layer (B) is then laminated with the latter onto the adhesive layer on the image-receiving sheet. (Meth) acrylic ester polymers and especially vinyl acetate polymers with a softening range of 80 to 180 ° C. are suitable for this type of transfer.

The thermoplastic polymer is preferably contained in the adhesive layer in a proportion of more than 50% by weight. It generally has a softening temperature in the range from 40 to 200, in particular 60 to 120 ° C. The adhesive layer can also contain UV absorbers, antistatic additives, inert fillers, optical brighteners, additives for increasing the stickiness and plasticizers. Suitable adhesive layers are described in US Pat. No. 5,049,476 and the older German patent applications P 42 04 950.4 and P 42 43 253.7. The adhesive layer is generally thicker than 1 µm; it usually has a layer weight of 2 to 30, preferably 4 to 12 g / m ² .

The image-receiving sheet (E) can be made of any suitable material that can withstand the conditions of lamination and pull-apart and that provides a suitable visual contrast to the transferred color image. Usually the material should be white. Plastic films, for example pigmented polyester films, plastic-coated papers, for example paper coated with polyethylene, wood, glass, metal and the like can be used. The material can have an adhesive pre-coating. A normal printing paper can also be used.

The lamination is carried out by placing the photopolymerizable material with its adhesive layer on the receiving sheet and guiding it through the nip of two heated laminating rollers under sufficient pressure. The lamination temperature is usually in the range of 60 to 130, preferably 70 to 110 ° C. The rollers can be the same or different temperature; the lamination speed is usually between 10 and 100, preferably 20 to 60 cm / min.

The photopolymerizable layer is exposed in a known manner through the transparent carrier film (A) before or after lamination. The exposure is usually carried out under a positive halftone color separation in the vacuum copying frame. Mercury vapor lamps are preferred as light sources. Light absorption filters can be used to reduce stray light.
After lamination and exposure, the image is developed by peeling the backing film uniformly from the receiver sheet at room temperature. Special devices for holding down or holding the receiver sheet during the peeling are not necessary because only moderate peeling forces are required. The pull-off angle should be at least 90 °. On removal, the entire undyed photopolymerizable layer (D) together with the exposed areas of the colored polymerizable layer with the carrier film are removed and the unexposed areas of the colored polymerizable layer remain with the entire adhesive layer on the image-receiving sheet. A positive image of the template is thus obtained.

Another photopolymerizable material with a differently colored polymerizable layer is laminated to the first partial color image by means of an adhesive layer and exposed through the corresponding color separation in the register to the first partial color image. The second partial color image is developed in the same way by peeling off the carrier film. A third and fourth partial color image can be added in the same way. Usually a four-color image is created from the Basic colors cyan (teal), magenta (purple), yellow and black built up. If desired, the surface of the finished image can be given a matt texturing, for example by embossing the glossy surface in contact with a rough surface, for example a matt film. For this purpose, the image and the matted film are passed together through a nip of a laminator. The surface texturing can be determined by selecting an appropriate matted material. Finally, the finished image can be cured by exposure with a suitable light source, if necessary with heating. A protective layer, as described, for example, in US Pat. No. 4,999,266, can also be laminated onto the surface of the finished image.

The following examples illustrate preferred embodiments of the invention. The quantities are usually given in parts by weight (pbw). Unless otherwise stated, quantitative ratios and percentages are to be understood in weight units.

example 1

A solution from 18.8 pbw Polyvinyl formal, average molecular weight 110,000, 7% vinyl alcohol units, 11% vinyl acetate units and 82% vinyl formal units ( ^(R) Formvar 15/95), 11.3 pbw Dipentaerythritol pentaacrylate and 5.6 pbw 2- (4-styrylphenyl) -4,6-bis-trichloromethyl-s-triazine in 1500 Gt Tetrahydrofuran and 450 pbw 1-methoxy-2-propanol is applied to the side of a 50 μm thick biaxially stretched and heat-set polyethylene terephthalate film which is adhesion-imparted according to US Pat. No. 4,391,767. The other side of the film was equipped with anti-blocking equipment. To drying for two minutes at 70 ° C., the photopolymerizable layer has a weight of 0.3 g / m ² .

One of the following coating solutions for the basic colors cyan, yellow, magenta and black is applied to four samples of the polyester film provided with the photopolymerizable layer in such a way that at least part of the undyed photopolymerizable layer remains undissolved: Cyan Gt Yellow gt Magenta Gt Black Gt Dipentaerythritol pentaacrylate 3.60 3.09 3.03 3.02 Polyvinyl formal average molecular weight 80,000, 24% vinyl alcohol units, 26% vinyl acetate units and 50% vinyl formal units ( ^(R) Formvar 12/85) 2.86 2.87 3.01 2.42 ^(R) Hostaperm blue B2G (Cl 74 160) 1.75 - - - Permanent yellow GR (Cl 21 100) - 1.33 - - Permanent carmine FBB (Cl 12 485) - - 1.58 - Carbon black ( ^(R) Printex 25) - - - 2.07 Tetrahydrofuran 93.00 79.95 78.28 78.05 1-methoxy-2-propanol 63.00 54.16 53.03 52.87 γ-butyrolactone 12.62 11.77 14.10 15.12

The color pigments are introduced into the solutions as dispersions. For this purpose, they are dispersed together with part of the polyvinyl formal in butyrolactone and ground to the desired particle size, ie an average particle diameter of 0.1 μm. Before coating each one Coating solution mixed well. The coatings are dried at 70 ° C for 2 minutes; then the optical densities of the individual layers have the following values: Cyan 1.3 yellow 1.0 magenta 1.4 black 1.6 The layer weights are 0.6 g / m ² .

An adhesive layer solution of the following composition is applied to each of the color layers: Gt Ammonium hydroxide (25%) 8.5 Sodium sulfite 1.4 Polyvinyl methyl ether ( ^(R) Lutonal M 40) 1.9 fumed silica, average particle size 3 µm 0.1 Copolymer vinyl acetate / crotonic acid (95: 5) 96.7 water 520.0 Ethanol 43.0 After drying, the adhesive layers each have a weight of 6.5 g / m ² .

The cyan film is laminated with its adhesive layer on a receiving sheet of paper at 105 ° C. The light-sensitive material is then exposed under a cyan-positive color separation through the carrier film using a 5,000 W copying lamp for 3 seconds. After exposure, the carrier film is removed from the receiver sheet deducted, the exposed areas of the color layer adhere to the carrier film and the unexposed areas remain together with the entire adhesive layer on the receiving sheet.

The yellow photosensitive color film is laminated in the same way on the cyan partial color image, then exposed under the corresponding yellow color separation and developed into the yellow partial color image by peeling off the carrier film. These process steps are repeated accordingly with the magenta and the black color film. An accurate four-color reproduction of the original is obtained.

The point rendering is at least 3 to 99% in a grid of 60 lines per cm. The yellowing in the non-image areas, measured with a blue filter, corresponds to an optical density of 0.01; it increases to 0.02 after 30 seconds after the backing film has been peeled off.

Examples 2 to 8

A cyan film is produced as described in Example 1, but with different photoinitiators in the photosensitive layer. The following table shows the photoinitiators, their color, their absorption maximum, the optimal exposure time and the background discoloration before and after the post-exposure. example initiator λ max (nm) Exposure time (s) Discoloration before after exposure 1 like example 1 371 3rd 0.01 0.02 2nd 2- (4-ethoxy-naphth-1-yl) -4,6-bis-trichloromethyl-s-triazine 388 5 0.01 0.02 3rd 2- (4-methoxy-styryl) -4,6-bis-trichloromethyl-s-triazine 379 6 0.01 0.02 4th Michler's ketone 366 60 0.01 0.02 5 2- (3,4-dimethoxy-phenyl) -4,6-bis-trichloromethyl-s-triazine 352 20th 0.01 0.02 6 2- (3,4,5-trimethoxyphenyl) -4,6-bis-trichloromethyl-s-triazine 337 70 0.01 0.02 7 2-biphenylyl- (4) -4,6-bis-trichloromethyl-s-triazine 332 25th 0.00 0.01 8th 4,4'-bis [2,4-bis-trichloromethyl-triazinyl (6)] diphenyl ether 331 30th 0.00 0.01

Example 9

In the cyan film according to Example 1, the amount of the monomer in the photopolymerizable layer is doubled, ie increased to 22.6 pbw. The optimal exposure time is still 3 s. The point reproduction is changed to 2 - 98%. The background discoloration of the four-color image to yellow is 0.02, with post-exposure 0.04 density units.

Example 10

Example 1 is repeated with the modification that the monomer in the photopolymerizable layer of the cyan film is replaced by the same amount of trimethylolpropane triacrylate. The optimal exposure time is 5 seconds. The background discoloration of the four-color image to yellow corresponds to 0.02, with post-exposure 0.03 density units.

Example 11

Example 1 is repeated with the modification that the binder in the photopolymerizable layer is replaced by the same amount of an ethyl methacrylate polymer (viscosity in 37.5% solution in toluene 7,500 mPa.s, acid number 0, Tg 63 ° C.). The exposure time is 5 seconds. The background discoloration of the four-color image to yellow corresponds to 0.01, with post-exposure 0.02 density units. The point rendering is 4 - 97%.

Comparative Example A

The procedure is similar to that in Example 1, but the photopolymerizable layer and the color layer are combined to form one layer. The coating solutions for the 4 base films have the following composition: Cyan Gt Yellow gt Magenta Gt Black Gt Dipentaerythritol pentaacrylate 3.90 3.82 3.55 3.61 Formvar 12/85 3.13 3.54 3.65 2.89 s-triazine derivative according to Example 1 0.98 0.95 0.78 0.96 Hostaperm blue B2G 1.90 - - - Permanent yellow GR - 1.64 - - Permanent carmine FBB - - 1.85 - Printex 25 - - - 2.48 Tetrahydrofuran 100.00 100.00 100.00 100.00 1-methoxy-2-propanol 68.00 68.00 68.00 68.00 γ-butyrolactone 19.00 19.00 19.00 19.00

The photopolymerizable color layers are produced in the same way as described in Example 1. The optical densities and layer weights are the same as stated there. The same adhesive layer is applied to the color layers as in Example 1.

The color foils are processed into a multicolor image in the same way as described in Example 1. The dot reproduction is 2 to 98%, the exposure time is 3 to 6 seconds depending on the color. The yellow background discoloration is 0.04 density units because the photoinitiator contained in the color layer is colored yellow. After 30 seconds of exposure, this value increases to 0.06 and is therefore no longer tolerable.

Comparative Example B

Comparative example A is repeated with the proviso that the s-triazine used as the photoinitiator is replaced by the same amount of the white compound 2-biphenylyl- (4) -4,6-bis-trichloromethyl-s-triazine. Dot rendering ranges from 2 to 98%, but exposure times from 14 to 28 seconds are required. The yellow background discoloration is 0.03 units; with post exposure it increases to 0.09 units.

Example 12

As described in Example 1, 4 color photosensitive films are prepared with the following coating solution: Cyan Gt Yellow gt Magenta Gt Black Gt Dipentaerythritol pentaacrylate 3.60 3.09 3.03 3.02 Formvar 12/85 2.86 2.87 3.01 2.42 Hostaperm blue B2G 1.75 - - - Permanent yellow GR - 1.33 - - Permanent carmine FBB - - 1.58 - Printex 25 - - - 2.07 Butanone 39.00 33.53 32.83 32.73 1-methoxy-2-propanol 87.75 75.44 73.86 73.64 4-hydroxy-4-methyl-2-pentanone 29.25 25.15 24.62 24.54 γ-butyrolactone 12.62 11.77 14.10 15.12

The color foils are processed as in Example 1 and give essentially the same results. The solvent mixture used in this example is preferred because the 4-hydroxy-4-methyl-2-pentanone contained therein the polyvinyl formal contained in the photopolymerizable underlayer as a binder does not dissolve. Since the 1-methoxy-2-propanol does not dissolve any of the polyvinyl formals used, less care needs to be taken to ensure that the underlayer is not dissolved.

Claims (15)

1. A photopolymerisable material having

   (A) a flexible transparent base film,

   (B) a coloured polymerisable layer which contains an organic binder, a compound which is polymerisable by a radical mechanism and which contains at least one ethylenically unsaturated terminal group, and a dye or a coloured pigment, and

   (C) an adhesion layer which contains a thermoplastic polymer and has a Tg of 25 to 100°C,

   characterised in that layer (B) does not contain a photoinitiator, that an uncoloured photopolymerisable layer (D) is disposed between the base film (A) and the coloured polymerisable layer (B) and contains a polymeric organic binder, a compound which is polymerisable by a radical mechanism and which contains at least one ethylenically unsaturated terminal group, and a photopolymerisation initiator, and that the cohesion of layers (B), (C) and (D) and the adhesion of these layers to each other and to the base film (A) is adjusted so that the adhesion (a₂) of the photopolymerisable layer (D) to the coloured layer (B) in the unexposed state is less than the adhesion (a₃) of the coloured layer (B) to the adhesion layer (C) and less than the adhesion (a₁) of the photopolymerisable layer (D) to the base film (A), and is less than the cohesions (c₁), (c₂) and (c₃) of layers (D), (B) and (C), and that the adhesion (a₃') of the coloured layer (B) to the adhesion layer (C) in the exposed state is less than the adhesion (a₁') of the photopolymerised layer (D) to the base film (A) and less than the adhesion (a₂') of the photopolymerised layer (D) to the coloured layer (B) and is less than the cohesions (c₁'), (c₂') and (c₃') of layers (D), (B) and (C).
2. A photopolymerisable material according to claim 1, characterised in that the coloured polymerisable layer (B) is not light-sensitive.
3. A photopolymerisable material according to claim 1, characterised in that the surface of the base film (A) on which the uncoloured layer (D) is situated has been pretreated to increase its adhesion.
4. A photopolymerisable material according to claim 3, characterised in that the surface has been pretreated by coating with an acrylic acid or methacrylic acid ester polymer.
5. A photopolymerisable material according to claim 1, characterised in that the compound which is polymerisable by a radical mechanism contains at least two ethylenically unsaturated terminal groups.
6. A photopolymerisable material according to claim 1, characterised in that the uncoloured photopolymerisable layer (D) has a weight of 0.05 to 3 g/m².
7. A photopolymerisable material according to claim 1, characterised in that the coloured polymerisable layer (B) has a weight of 0.1 to 5 g/m².
8. A photopolymerisable material according to claim 1, characterised in that the adhesion layer (C) has a weight of 2 to 30 g/m².
9. A photopolymerisable material according to claim 1, characterised in that the coloured polymerisable layer (B) is thicker than the uncoloured photopolymerisable layer (D).
10. A method of producing a coloured image, characterised in that a photopolymerisable material according to claim 1 is laminated, under pressure and at elevated temperature, on to an image-receiving sheet (E) with its adhesion layer (C), the laminate obtained is exposed image-wise through the base film (A), and the base film together with the photopolymerisable layer (D) and the exposed regions of the coloured polymerisable layer (B) is peeled off from the receiving sheet, wherein the adhesion of the adhesion layer (C) to the image-receiving sheet (E) in the unexposed state (a₄) is greater than the adhesion (a₂) of the photopolymerisable layer (D) to the coloured layer (B), and in the exposed state (a₄') is greater than the adhesion (a₃') of the coloured polymerisable layer (B) to the adhesion layer (C).
11. A method according to claim 10, characterised in that a partial colour image is produced by using a photopolymerisable material, the coloured polymerisable layer (B) of which is coloured in a primary colour of the multicolour print, and effecting the exposure with a colour separation for the same primary colour.
12. A method according to claim 10, characterised in that a photopolymerisable material of another primary colour is laminated on to the first partial colour image and the exposure is effected in register with the first partial colour image and the same steps are optionally repeated with at least one further primary colour.
13. A method according to claim 10, characterised in that the photopolymerisable material is laminated on to the receiving sheet at a temperature within the range from 60 to 130°C.
14. A method according to claim 10, characterised in that the coloured image on the image receiving material is covered with a protective coating.
15. A method according to claim 10, characterised in that the coloured image obtained on the image receiving sheet after peeling off the base film is hardened by exposure without a pattern.

Images